Reedit: "A minimalist, elastic and read-only Reddit web-app client, that lets you create custom 'Channels' with up to 3 subreddits each." Probably the first web application I've used that doesn't make me long for something native. Fantastic work.

I think general the techniques for achieving performance are pretty much the same. For example, on Windows 8 which uses HTML5/JS as an option for app development, a lot of the Windows-isms are built on existing HTML5 solutions. Async built ontop of JS promises, view state swapping on top of Media Queries, etc.